Is there any grammar to explain how some irregular verbs like "input" and "output" have two past forms? I've seen both "input/inputted" and "output/outputted" in written and spoken English. Based on that "in" and "out" are just prefixes and the core verb is "put" that is only irregular, how is that correct and possible?

I found this article Verbs with two different past tense forms by Oxford Dictionary and so I just guess they are exceptions, right?

  • Seems to me the page you linked to explains the source of the problem: some people form the past tense for words like this based on the second element of the compound; others just treat it as a regular past tense. There are actually many more verbs with alternative past tense forms, not all of which can be explained the same way, though. For example, in British English we can choose between "spelled" and "spelt". (Only the former is used in American English.)
    – rjpond
    Commented Aug 29, 2017 at 18:07
  • @rjpond I'm familiar with the different spelling of Br.E and Am.E. Commented Aug 29, 2017 at 18:16
  • Of course. But is it a spelling question? You see, I wasn't thinking of it as such. I pronounce "spelled", "burned" etc with /d/ and "spelt", "burnt" etc with /t/. But perhaps others use the "-ed" spellings together with /t/ pronunciations, I'm not sure.
    – rjpond
    Commented Aug 29, 2017 at 18:27
  • @rjpond I doubt it. The way you pronounce them is perfectly correct. However, I meant that choosing between different spelling of a word and choosing a different form of a word are two different things. Commented Aug 30, 2017 at 3:55

1 Answer 1


Because English is a natural language there are lots of inconsistencies.

The "put" element is indeed the common verb, and that verb is irregular, with the past and past participle the same as the bare infinitive.

The verb "input" is quite old, and in older senses (meaning "impose") it is similar to put. However, prior to computers, the word was quite rare. In the new sense of "put data into a computer" both "he has input some data" and "he has inputted some data" are in use by native speakers, and so both are correct.

You can't justify this based on logic, because language is not logical. If you need a justification, you can say "to input" is derived not as "in + put" but by from the noun "an input", and verbs formed from nouns are all regular.

As noted in the article you link:

In these instances, you should use the past form that comes most naturally to you, while bearing in mind that other people may use a different one.


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